After an amputation, and once healing is completed, a permanent or "definitive" prosthesis is assembled by the prosthetic. The permanent prosthesis for an above-knee amputation includes a socket made from a cast that matches the shape of the stump. A prosthetic limb attached to the bottom of the socket typically carries a knee joint and a prosthetic foot.
There is a constant need to provide an above-knee prosthesis which is comfortable at all times when in use. To this end, it has been common for a liner to be worn by a patient to protect the skin from direct contact with the inside of the socket, where discomfort is often a problem. Recently, the use of softer, more flexible plastic materials for the socket has avoided the need for wearing a liner. In either event, the socket is custom-made with a removable valve installed in a housing in the bottom. The value is removed to allow the prosthetic limb wearer to don the prosthesis through a "pulling-in" process which involves threading a tubular knit pull sock through the valve hole after previously slipping the opposite end over the residual limb. A one-way relief valve which can be operated by finger pressure to exhaust any air entrapped inside the socket is installed in the housing after donning. In this way, the user can use the air relief valve to exhaust residual air from the socket after donning the prosthesis and at any time thereafter to relieve discomfort caused by entrapped air between the skin and the inside of the socket.
There have been several prior art attempts to provide a secure, leak-free valve system for a prosthetic socket, but none has proved entirely satisfactory. The problem of developing a leak-free housing is particularly difficult when using the softer, more flexible vacuum-formed plastics, such as polyethylene, for the socket material. These materials are desirable for their comfort, but they can be difficult to bond to a rigid valve housing in a way that maintains the seal under pressures applied during constant use.
In one prior art valve system, a thin rubbery gasketing material is applied around the exterior of a valve housing attached to the cast or model. When the plastic socket material is vacuum-formed over the valve housing and the model, the gasketing material is intended to form a seal between the valve housing and the socket. However, during use, this valve system is prone to leak air between the hard plastic valve housing and the flexible polyethylene socket.
Another prior art valve system uses a hard plastic valve housing with vertical notches in its exterior surface and a horizontal O-ring near the bottom of the housing. The notches and O-ring are intended to form a mechanical interlock with the vacuum-formed socket, but this valve system also is prone to leaking between the valve housing and the plastic socket.
More recently, a valve housing has been made with a downwardly tapered, conical outer surface and an O-ring located in the conical surface at the interface for interlocking with the vacuum-formed plastic. This arrangement also does not appear to provide the mechanical interlock necessary for a secure leak-free valve during long term use of the socket.